Reference is made to my co-pending application entitled HIGH-PRESSURE DUAL-FEED-RATE INJECTOR PUMP WITH AUXILIARY SPILL PORT, filed on the same day as the present application and directed to related subject matter. The disclosure of such co-pending application is incorporated by reference in this application as if fully repeated herein.
Some fuel injector pumps of the mechanical spill type rely on a sleeve separate from the bushing and slidable on or relative to the pump plunger to contribute to the valving of fuel, in order for example to combine spill valving with the sequential distribution of fuel from a single pump to two or more injection nozzles at two or more separate cylinders of a diesel engine. In such "sleeved" assemblies, there is one pattern of relative motion between the pump plunger and the bushing and an altered pattern of relative motion between the plunger and the sleeve.
However the type of plunger and bushing pumps to which the invention relates are of a another sub-type which may be referred to as "sleeveless" in that no sleeves are used for spill valving; rather the pump's own spill valving functions (as distinguished from the valving functions of a check valve or an injection valve associated with the pump) are entirely accomplished by interactions between (1) edges and cut-outs formed on the pump plunger and (2) orifices opening into the pump bore from the low pressure passages. Such sleeveless pumps or plunger and bushing devices are typically associated with the use of one pump for each cylinder of the engine.
Fuel injectors of the sleeveless mechanical spill type include a fuel pump and an injection nozzle associated with the fuel pump. The fuel pump includes a pump cylinder or "bushing" and a pump plunger reciprocable in the bushing. Such a "plunger and bushing" ("p&b") assembly defines a pump chamber open at one end for the discharge of fuel during a pump stroke and for fuel intake during a suction or fill stroke of the plunger. The injection nozzle is associated with a valve body having a spray outlet at one end for the discharge of fuel at the nozzle tip. The injection valve is movable in the valve body between open and closed positions to control flow from the spray outlet. The injection valve is spring-biased to a closed position and openable when such discharge of fuel during a pump stroke reaches a given high pressure. The injection valve then remains open until pressure drops to a closing pressure somewhat below the opening pressure. The closing pressure is below the opening pressure because the injection valve face area subject to injection pressures is somewhat greater when the injection valve is open and unseated than when it is closed and seated.
Fuel is supplied to the pump and excess fuel is returned from the pump to a reservoir through low pressure passages communicating with the pump chamber. The low pressure passages constitute spill passages for spilling the fuel discharged by the pump stroke of the plunger. The spill passages intersect the bushing bore at spill ports. The flow areas of the spill ports are each large enough that the fuel is spilled back into the low pressure supply system at a rate high enough to prevent the discharge of fuel, resulting from the pump stroke, from reaching the given pressure at which the injection valve opens to commence fuel injection, or from remaining above the somewhat lower given pressure at which the open injection valve closes.
The length of the injection portion of the pump stroke is adjustable by suitable means including a port-closing edge and a port-opening edge each associated with its own one of a pair of ports opening into the plunger-receiving bore of the bushing. The port-closing and port-opening edges may also be referred to as land edges or as control edges. The port-closing and port-opening edges have different helix angles whereby the interval between port closing (of one port of the pair) and port opening (of the other port in the pair) in each pumping stroke is increased as the angular position of the plunger and the two edges around the axis of the plunger is adjusted throughout a range of adjustment to increase the injection portion of the pump stroke throughout a corresponding range of engine loads. One of these two edges may have a helix angle of zero.
Fuel injection, that is, delivery of fuel to the injection nozzle downstream of the plunger chamber at a high enough pressure to cause the injection valve to open and to remain open, occurs during that part of each stroke of the pump plunger during which both the ports associated with the pair of port control edges are closed or covered by their associated control edges to thereby establish, between the closing of one port and the opening of the other, the fuel delivery effective stroke, i.e., the injection portion of the pump stroke.
The initial rate of fuel injection has a profound influence on the maximum combustion pressure and temperature generated in diesel engine combustion chambers during engine operation. When combustion pressure and temperature are elevated above certain limits, nitrogen is oxidized to form nitrous oxide. Ignition delay is the principal reason for the high pressure and temperature generated. Improved ignition quality of fuel and higher compression pressures can reduce the ignition delay period, but there is a limit to the improvement that can be achieved with improved fuel quality, which also carries a cost penalty. Higher compression pressures also have the adverse effect of increasing maximum combustion pressure which in turn tends to increase the formation of nitrous oxide.